The invention relates in general to respirators and in particular to a new and useful protective breathing apparatus with breathing air circulation and with addition of oxygen alone through a lung controlled valve.
A similar protective breathing apparatus is described in German patent application No. 919,628. In the known protective breathing apparatus, the breathing bag, the lines carrying breathing gas, and the regeneration unit are flushed with pure oxygen before applying the mouthpiece so that the wearer of the apparatus can inhale from a full breathing bag flushed with oxygen and return his exhaled air into it again. If a larger amount of breathing air is inhaled, the collapsing breathing bag actuates a lever mechanism which opens a valve to add oxygen to the inhale line. The breathing bag is kept to a minimum volume by the inflowing oxygen. When the wearer of the known protective breathing apparatus puts it on and exhales his first full breath into the protective breathing apparatus, then, assuming the worst case, the nitrogen component from his lungs mixes with the oxygen in the protective breathing apparatus. While a part of this mixture leaves the breathing circulation through a pressure relief valve, because breathing bag was already filled by the oxygen flushing the system, oxygen from the supply in the breathing bag is constantly consumed by the apparatus wearer during the subsequent inhale phases, and a constant oxygen depletion occurs in the protective breathing apparatus circulation during the subsequent breathing cycles. Especially at low volume inhale phases it may take several breathing cycles to empty the breathing bag to the point where the lung controlled valve responds and feeds pure oxygen into the breathing bag. In the meantime, however, the oxygen depletion can have progressed so far that the last inhaled breaths no longer contain enough oxygen for the apparatus wearer. This oxygen depletion, which is equivalent to a nitrogen enrichment, can bring the apparatus wearer into undesirable situations.
Beyond this, the dosing parts and supply lines needed to flush the breathing circulation with oxygen are costly, require additional space in the apparatus housing and increase the weight of the protective breathing apparatus.